Comparison of continuous and fractionated illumination during hexaminolaevulinate-photodynamic therapy.

Objective: This experimental study aimed to compare continuous and fractionated illumination to optimize hexaminolaevulinate (HAL)-photodynamic therapy (PDT) in a rat tumour model with advanced ovarian cancer.

Materials And Methods: Intraperitoneal 10(6) Nu Tu-19 cells were injected in 36 female rats Fisher 344. Peritoneal carcinomatosis was obtained 26 days post-tumour induction. Four hours post-intraperitoneal HAL (Photocure ASA, Oslo, Norway) injection, two schemes of PDT were performed at 30 mW cm(-2) on a 1cm(2) area: fractionated illumination (n=16) with a on-off cycle ("on": 2 min and "off": 1 min) until a fluence of 30 J cm(-2) was delivered, and continuous illumination (n=20) with a fluence of 45 J cm(-2). Laser light was generated using a 532 nm KTP laser (Laser Quantum, Stockport, UK). Biopsies were taken 24h after treatment. Semi-quantitative histology was performed. Necrosis value was determined-0: no necrosis to 4: full necrosis.

Results: HAL-PDT was efficient in producing necrosis irrespective of the scheme (NV=3.34+/-0.91). Tumour destruction was superior with fractionated illumination compared to continuous illumination (3.67+/-0.70 vs. 3.10+/-0.94) (p<0.05).

Conclusion: Fractionated illumination during photodynamic therapy was shown to improve tumour response. Fractionated illumination with short intervals should be considered for an effective PDT of advanced ovarian cancer.